To this end, we also note that Mauring et. al [1]} observed fluorescence enhancement of the blue fluorescent protein (BFP) with hydrostatic pressure. The coupling of BFP chromophore with the rest of the protein is different as compared to GFP because of the His66 substitution, which leads to smaller number of hydrogen bonds [2]}, [3]}, [4]}. Due to smaller number of hydrogen bonds, the fluorescence lifetime and the quantum yield of BFP is much smaller compared to GFP. They find that the fluorescence quantum yield increases with pressure without a change in the shape of emission spectra, results very similar to our results for GFP. They further attribute the increase in fluorescence quantum yield with pressure to the inhibition of fast quenching processes due to stabilization of hydrogen bond between the chromophore and the rest of the protein. We expect that the decrease in anisotropy may reflect the effect of pressure on the radiative and non-radiative decay processes arising due to pressure-temperature effect on the H-bonding environment around the chromophore. Our current experimental setup does not allow us to perform time-resolved experiments, which on the other hand, would have been an ideal way to resolve these issues, and should be explored in future.
